Rear Main Seal Leak

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rubio9800

Greasemonkey
Oct 10, 2020
242
110
43
California
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak (rope type)

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

I recently switched to 15w40(synthetic), hoping it could slow it down. Would conventional be better in this case?

thanks
 
Last edited:

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,872
3,050
113
West Michigan
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak.

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

thanks
This is a very common problem on all older GM engines. It’s one of the reasons I upgraded to an LS engine.....My garage floor is dry.

The shop is correct. Replacing the seal will not guarantee the leak will be fixed but it should significantly reduce leakage if they do it right and use the right gaskets / seals.
 
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g0thiac

G-Body Guru
Sep 6, 2020
939
582
93
Hey folks,

My 81GP is leaking, shop confirmed rear main seal, but was not comfortable in replacing as no guarantee it would stop the leak (rope type)

Definitely can’t do this on my own, has anyone dealt with this?

265 engine (just a weekend cruiser, not interested in high HP)

I recently switched to 15w40, hoping it could slow it down.

thanks
Swap it out with a 305 or 350. 265's aren't worth rebuilding unless it has low mileage.
 

g0thiac

G-Body Guru
Sep 6, 2020
939
582
93
This is a very common problem on all older GM engines. It’s one of the reasons I upgraded to an LS engine.....My garage floor is dry.

The shop is correct. Replacing the seal will not guarantee the leak will be fixed but it should significantly reduce leakage if they do it right and use the right gaskets / seals.
He should go LS because he wants to do that, not because of a rear main leak. Because the money you'd spend on paying someone to swap the motor, computer and install the wiring out exceeds what a straight 350 swap would. Both my SBC's are over 30 years old, both over 150,000KM and have never had the seals worked on.
 
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Jorge1958

Master Mechanic
Mar 2, 2019
380
214
43
Columbia City Oregon
U say your using 15w40 motor oil. I hope its not delo 400 or another diesel type oil. Very high detergent and can damage internal engine parts. Get a can of Lucas oil stop leak. Also 20w50 conventional motor oil. Try that. Should at least slow it down.
 
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rubio9800

Greasemonkey
Oct 10, 2020
242
110
43
California
U say your using 15w40 motor oil. I hope its not delo 400 or another diesel type oil. Very high detergent and can damage internal engine parts. Get a can of Lucas oil stop leak. Also 20w50 conventional motor oil. Try that. Should at least slow it down.
rotella t6, yea it’s diesel.
i’ll try to do 20w50 today or tomorrow
 
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g0thiac

G-Body Guru
Sep 6, 2020
939
582
93
it has 80k, i guess engine swap would be the only solution?
80,000KM or miles? You could rebuild it, but honestly the cost of a kit would be around the same of a 305 motor, if not 350 too with similar wear on it.
 

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,872
3,050
113
West Michigan
He should go LS because he wants to do that, not because of a rear main leak. Because the money you'd spend on paying someone to swap the motor, computer and install the wiring out exceeds what a straight 350 swap would. Both my SBC's are over 30 years old, both over 150,000KM and have never had the seals worked on.
I’m not suggesting he swap an LS to fix the issue. The OP clearly stated he doesn’t need extra power and is happy with the performance of the anemic 265. I’m merely stating a fact that the older designs suck.
 
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